Where can I find a stencil of Texas?

Try online. You could make your own stencil by printing out the outline of Texas. Hope this helps. (I actually did this one time.)

I bought a wood cutout of Texas at Wal-Mart. I traced around it to make a stencil. I still use that cutout to trace around for other things.

Depending on size, your local library may have a "projector" you could either connect to your laptop, on location or, check out. Then put your paper/cardboard on a wall and copy/trace it. I recently did this and made couple of 6 foot Texas shaped bar tables for myself and a friend.

To find my outline I did a search online for "line drawing" and Texas. Then you use the projector's zoom and/or the projector's distance to wall placement to get the size you need.